OH Overtone Research Articles

Comparison of macro x‐ray fluorescence and reflectance imaging spectroscopy for the semi‐quantitative analysis of pigments in easel paintings: A study on lead white and blue verditer

AbstractMacroscopic x‐ray fluorescence imaging spectroscopy (MA‐XRF) and reflectance imaging spectroscopy (RIS) are important tools in the analysis of cultural heritage objects, both for conservation and art historical research purposes. The elemental and molecular distributions provided by MA‐XRF and RIS respectively, are particularly useful for the identification and mapping of pigments in easel paintings. While MA‐XRF has relatively established data processing methods based on modeling of the underlying physics, RIS data cannot be modeled with sufficient precision and its processing has considerable room for improvements. This work seeks to improve RIS data processing workflows in the short wavelength infrared range (SWIR, 1000–2500 nm) with a novel method that fits Gaussian profiles to pigment‐specific absorption features, and we compare its performance to MA‐XRF for the task of semi‐quantitative pigment mapping, evaluating their limits of detection (LODs) and the matrix effects that affect their signals. Two pigments are considered in this work, lead white and blue verditer, which are mapped in SWIR RIS using the first overtone of OH stretching of their primary compounds, hydrocerussite (Pb3(CO3)2(OH)2) and azurite (Cu3(CO3)2(OH)2), at 1447 and 1497 nm respectively, and in MA‐XRF using the Pb‐L and Cu‐K fluorescence signals. The methods are evaluated using two sets of custom‐prepared paint samples, as well as a 16th‐century painting, discussing the identification, mapping, and semi‐quantitative analysis of the considered pigments. We found SWIR RIS to be a pigment‐specific method with a longer linear range but inferior LODs and penetration depth when compared to MA‐XRF, the latter is often not capable of discriminating between different pigments with identical elemental markers. We furthermore present a novel color scale that allows the simultaneous visualization of signals above and below a confidence limit.

Absorption cross-sections for the 5th and 6th vibrational overtones in a series of short chained alcohols using incoherent broadband cavity enhanced-absorption spectroscopy (IBBCEAS)

Absorption cross-sections for the 5th (6 ← 0) and 6th (7 ← 0) OH overtones for gas-phase methanol, ethanol, and isopropanol were measured using a slow flow cell and Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy (IBBCEAS). Measurements were performed in two wavelength regions, 447–457 nm, and 508–518 nm, using two different instruments. The experimental results are consistent with previous computational predictions of the excitation energies for these transitions. Treating the OH stretch as a local mode allowed for calculation of the fundamental vibrational frequency (ωe), anharmonicity constant (ωexe), and the vertical dissociation energy (VDE) for each alcohol studied. The fundamental vibrational frequency is 3848 ± 18 cm−1, 3807 ± 55 cm−1, and 3813 ± 63 cm−1 for methanol, ethanol, and isopropanol, respectively. The anharmonicity constant was measured to be 84.8 ± 2.1 cm−1, 80.2 ± 5.9 cm−1, and 84.4 ± 6.8 cm−1 for methanol, ethanol, and isopropanol, respectively. The OH vertical dissociation energy was measured to be 499.4 ± 18.4 kJ/mol, 518.0 ± 56.7 kJ/mol, and 492.7 ± 59.9 kJ/mol. The spectroscopically measured values are compared to thermodynamically measured OH bond dissociation energies. The observed differences in previous measurements of the bond dissociation energies compared to the values reported herein can be explained due to the difference between vertical dissociation energies and bond dissociation energies. If the OH overtone stretching mode is excited in methanol to either the 5th or 6th overtone, the bimolecular reaction between methanol and O2 becomes thermodynamically feasible and could contribute to formation of methoxy and HO2 radical under the proper combination of pressure and temperature.

Near-Infrared Spectroscopy Study of OH Stretching Modes in Pyrophyllite and Talc

Pyrophyllite and talc are both tetrahedra–octahedra–tetrahedra (TOT)-type phyllosilicates, but differences can be found in the stacking mode of the layers and the ion occupation. Fourier transform infrared spectroscopy was used to differentiate between pyrophyllite and talc. In the 400–600 cm−1 region, pyrophyllite exhibits six peaks, while talc only exhibits five peaks. In the 1000–1200 cm−1 region, pyrophyllite exhibits three clear peaks at approximately 1051, 1070, and 1121 cm−1; while talc only exhibits one strong peak near 1020 cm−1. The differences between pyrophyllite and talc in the near–infrared (NIR) region are clear in the 4000–4700 cm−1 region, and pyrophyllite exhibits an intense peak around 4615 cm−1, which is attributed to the combination of the OH and Si-O-Si stretching bands. Talc has a maximum peak located near 4324 cm−1, which is attributed to the OH stretching vibration. In addition, talc has a secondary peak near 4366 cm−1. Talc has two other weaker peaks around 4054 and 4180 cm−1. The 7000–7250 cm−1 region exhibits the first fundamental overtone of the OH group stretching vibrations. The common characteristic band of these two minerals is 7175–7183 cm−1. The first overtone of OH stretching vibrations can also be generated by adjacent peaks in the fundamental overtones. The peaks of these two minerals around 7094 cm−1 appear to be a combination of 3630 (±5) cm−1 and 3642 (±3) cm−1.The factor of the first fundamental overtone of the OH group stretching vibration is 1.95 (±0.003). Therefore, the characteristic peaks in the mid-infrared (MIR) and NIR regions can be used to distinguish between pyrophyllite and talc, providing a research basis for further exploration in related geological areas.

Near-Infrared Spectroscopy Study of Serpentine Minerals and Assignment of the OH Group

Three different kinds of serpentine mineral samples were investigated using Fourier transform near-infrared spectroscopy (FTNIR). The results show that there are obvious differences in the characteristic infrared spectra of the three serpentine group minerals (lizardite, chrysotile, and antigorite), which can easily be used to identify these serpentine minerals. The combination of weak and strong peaks in the spectrum of lizardite appears at 3650 and 3690 cm−1, while the intensities of the peaks at 4281 and 4301 cm−1 (at 7233 and 7241 cm−1, respectively) are similar. A combination of weak and strong peaks in chrysotile appears at 3648 and 3689 cm−1 and at 4279 and 4302 cm−1, and a single strong peak appears at 7233 cm−1. In antigorite, there are strong single peaks at 3674, 4301, and 7231 cm−1, and the remaining peaks are shoulder peaks or are not obvious. The structural OH mainly appears as characteristic peaks in four regions, 500–720, 3600–3750, 4000–4600, and 7000–7600 cm−1, corresponding to the OH bending vibration, the OH stretching vibration, the OH secondary combination vibration, and the OH overtone vibration, respectively. In the combined frequency vibration region, the characteristic peak near 4300 cm−1 is formed by the combination of the internal and external stretching vibrations and bending vibrations of the structural OH group. The overtone vibrations of the OH stretching vibration appear near 7200 cm−1, and the practical factor is about 1.965. The near-infrared spectra of serpentine minerals are closely related to their structural differences and isomorphous substitutions. Therefore, near-infrared spectroscopy can be used to identify serpentine species and provides a basis for studies on the genesis and metallogenic environment of these minerals.

Local mode interpretation of the OH overtone spectrum of 1:1 phyllosilicates

Abstract. Although OH overtone bands of 1:1 phyllosilicates are commonly observed in their near-infrared (NIR) spectra, their interpretation in terms of transitions between specific vibrational states is still uncertain. This situation can be traced back to the coupled nature of the fundamental OH-stretching modes involving the interlayer OH groups of 1:1 phyllosilicates. In this case, the overtone spectra cannot be directly related to their fundamental counterparts observed in the mid-infrared (MIR) spectra. In the present study, we use a parameterized quantum-mechanical approach to compute the vibrational frequencies related to the fundamental and overtone bands in serpentine group and kaolinite group minerals. The simple model is based on a description of the vibrational properties of a cluster of OH groups in terms of harmonically coupled anharmonic oscillators. The comparison of the theoretical results with experimental observations makes it possible to interpret most of the salient features of the overtone spectrum of 1:1 phyllosilicates. Unlike the bands observed in the MIR spectra, the overtone bands observed between 7000 and 7300 cm−1 are related to local transitions from the ground state to the second excitation level of OH groups, whereas the weaker bands observed between 7300 and 7400 cm−1 involve a double excitation to the first vibrational level of OH oscillators. The results also support the assignment of specific overtone bands to the occurrence of substituted divalent cations of transition elements in serpentine group minerals.

Near Infrared and Aquaphotomic analysis of water absorption in lactate containing media.

Increased concentrations of lactate levels in blood are often seen in patients with life-threatening cellular hypoperfusion or infections. State-of-the-art techniques used in clinical practice for measuring serum lactate concentrations rely on intermittent blood sampling and do not permit continuous monitoring of this all important parameter in critical care environments.In recent years, Near Infrared (NIR) Spectroscopy has been established as a possible alternative to existing methods that can mitigate these constraints and be used for non-invasive continuous monitoring of lactate. Nevertheless, the dominant absorption of -OH overtone bands of water in the NIR presents a challenge and complicates the accurate detection of other absorbers such as lactate. For this reason, comprehensive analysis of the -OH overtone bands with systematic lactate concentration changes is essential. This paper reports on the analysis of NIR spectra of two aqueous systems of varying concentrations of lactate in saline and whole blood using the principles of Aquaphotomics.The results show distinctive conformational and structural differences in lactate-water binding, which arise due to the molecular interactions of bonds present in respective solvents.

The spectroscopic search for water in barite group sulfates.

This study examines the mid and near infrared spectra of a suite of natural and synthetic powdered minerals of the isostructural barite mineral group. The mid-infrared (MIR) spectra are wholly compliant with anhydrous high purity anglesite, celestine and barite. The complementary near-infrared (NIR) spectra contain bands at ca 1.9 μm (5263 cm-1) and ca 1.4 μm (7140 cm-1) assigned to the (H2O) v2 (antisymmetric stretch)+v3 (bending vibration) combination band and overtones of the fundamental OH stretching modes respectively. Peak-fitting of the ca 4660-6000 cm-1 region of interest reveals four shoulders to the (H2O) (v2+v3) combination which are systematically ordered with respect to interstitial metal covalent radius: [PbSO4] (lowest wave number) → [SrSO4] → [BaSO4] (highest wave number). These bands are assigned to (M2+-O-H) surface complexation of water with the sulfates. It is further interpreted that the two good-to-perfect cleavages in the mineral group with resultant variation in (M2+ - O - H) bond lengths accounts for the existence of the four bands and explain why absorption strength at ca 1.91 μm (5236 cm-1) is not a reliable indication of the overall abundance of water in sulfate minerals. Spectral interpretation within the vicinity of the water combination ca 1.91 μm (5236 cm-1) is further complicated by the presence of a higher wavenumber (v1+4v3) sulfate combination and the appearance of a band interpreted as the (5v3) overtone of [SO42-]. The results are discussed in the light of these findings.

The Nature of Laponite: Pure Hectorite or a Mixture of Different Trioctahedral Phases?

A series of laponites and synthetic OH- and fluorinated hectorites prepared from hydrothermal and melting experiments at both industrial and laboratory scale were examined with XRD and FTIR (MIR and NIR) to determine their mineralogical composition and possible compositional heterogeneity. The end materials contained both Li- and Na-bearing phases. The industrial hydrothermal OH-smectites prepared at low temperatures consist of random mixed layer hectorite-stevensite-kerolite with about 40–50% hectorite layers, the remaining being stevensite and kerolite at roughly equal proportions. The FTIR spectra of these smectites contain, besides the main Mg3OH stretching/overtone bands at 3695–3690 and 7225–7214 cm−1, respectively, additional OH overtone bands at ~3716 and 7265 cm−1 (hydrated state). These bands might be linked to Mg2LiOH stretching modes. The melt-derived smectites are kerolite-free but still contain stevensite layers, although the preparation methods involved heating in the excess of 1000 °C. In these smectites Li might be partitioned to both octahedral and interlayer sites. Subsequent annealing of the melt-derived Mg-Li smectites caused migration of the exchangeable Li to the vacant octahedral due to the Hofmann-Klemen effect and thus decrease of the layer charge, as was indicated by the νO-D method. Hydrothermal synthesis of Mg-Li smectites at high temperature (400 °C) and pressure (1 kbar), yielded pure hectorite without stevensite or kerolite domains.

Anharmonic calculations of frequencies and intensities of O[sbnd]H stretching vibrations of (R)-1,3-butanediol conformers in the fundamentals and first overtones by density functional theory

The frequencies and absorption intensities of the five kinds of conformers of 1,3-butanediol with the same carbon skeleton (GG′) were calculated by anharmonic calculation for the fundamentals and first overtones of OH stretching vibrations. The four kinds of conformers form intramolecular hydrogen bonds and one conformer did not. Intramolecular hydrogen bond formation shifted the frequency of fundamental and first overtone of H-bonding OH stretching vibration to the lower frequency. The absorption intensities of the fundamentals as well as the vibrational anharmonicities increased upon hydrogen bond formation, while the intensities of first overtones decreased. The differences of conformers were clearly seen in the frequencies of the first overtones of free OH.

Dynamics of Changes in the Infrared Spectrum of Distilled and Heavy Water upon Exposure to an Electron Beam of Nanosecond Duration

The absorption spectra of distilled and heavy water upon exposure to an electron beam of nanosecond duration are investigated. The changes in the absorption spectrum of distilled water after exposure to an electron beam are that the absorption band of valence vibrations of the OH groups becomes broadened, the amplitude of the valence asymmetric band increases, and a shift of the absorption maximums toward shorter wavelength frequencies and an increase in the amplitudes with insignificant band broadening are observed for absorption bands comprised of the sum of deformation and libration vibrations of water molecules and the deformation band of water. The changes in the absorption spectrum of heavy water after its irradiation with an electron beam consist in that the band of valence vibrations of the OH groups of the H2O and HDO molecules is broadened, while the absorption band of the OH overtones of the deformation vibrations of the HDO molecule becomes stronger and the absorption range is preserved. A shift of the absorption maximum toward higher frequencies is observed for the deformation vibrations of the H2O and HDO molecules of heavy water, and the maximum of deformation vibrations of the D2O molecules remains unchanged.

Effects of intermolecular interactions on absorption intensities of the fundamental and the first, second, and third overtones of OH stretching vibrations of methanol and t-butanol‑d9 in n-hexane studied by visible/near-infrared/infrared spectroscopy

Visible (Vis), near-infrared (NIR) and IR spectra in the 15,600–2500cm−1 region were measured for methanol, methanol-d3, and t-butanol-d9 in n-hexane to investigate effects of intermolecular interaction on absorption intensities of the fundamental and the first, second, and third overtones of their OH stretching vibrations. The relative area intensities of OH stretching bands of free and hydrogen-bonded species were plotted versus the vibrational quantum number using logarithm plots (V=1–4) for 0.5M methanol, 0.5M methanol‑d3, and 0.5M t-butanol-d9 in n-hexane. In the logarithm plots the relative intensities of free species yield a linear dependence irrespective of the solutes while those of hydrogen-bonded species deviate significantly from the linearity. The observed results suggest that the modifications in dipole moment functions of the OH bond induced by the formation of the hydrogen bondings change transient dipole moment, leading to the deviations of the dependences of relative absorption intensities on the vibrational quantum number from the linearity.

Conformational switching in pyruvic acid isolated in Ar and N₂ matrixes: spectroscopic analysis, anharmonic simulation, and tunneling.

Monomers of pyruvic acid (PA) isolated in cryogenic argon and nitrogen matrixes were characterized by mid- and near-infrared spectroscopy. Interpretation of the experiments was aided by fully anharmonic calculations of the fundamental modes, overtones, and combinations up to two quanta, including their infrared intensities. The initially dominating PA conformer (Tc) has a cis CCOH arrangement and is stabilized by a strong intramolecular H-bond. Selective near-infrared excitation of Tc at the first OH overtone (6630 cm(-1) in Ar, 6643 cm(-1) in N2) induced a large scale conformational conversion to the higher-energy conformer (Tt) with trans CCOH arrangement. Tt was then converted back to Tc by selective NIR irradiation at the first Tt OH overtone (6940 cm(-1) in Ar, 6894 cm(-1) in N2). In N2 matrix, the Tt form was stabilized due to interaction between the OH group and the matrix molecules. This stabilization manifested itself in the absence of Tt → Tc relaxation and in a considerable change of the vibrational Tt signature upon going from argon to nitrogen matrix. In argon, the Tt form spontaneously decayed back to Tc in the dark (characteristic lifetime +16 h). In the presence of broad-band near-infrared light, the Tt → Tc relaxation speed considerably increased. The decay mechanisms are discussed.

Water molecular system dynamics associated with amyloidogenic nucleation as revealed by real time near infrared spectroscopy and aquaphotomics.

The formation of amyloid fibrils proceeds via a nucleation-dependent mechanism in which nucleation phase is generally associated with a high free energy resulting in the rate-limiting step. On the basis of this kinetic feature, the nucleation is one of the most crucial phases controlling the pathogenesis of amyloidoses, but little is known about the details of how protein molecules and surrounding environment vary at this stage. Here, we applied near infrared (NIR) spectral monitoring of water structural changes in real time during the nucleation-dependent fibrillation of insulin. Whilst multivariate spectral analysis in the 2050–2350 nm spectral region indicated cross-β formation, characteristic transformations of water structure have been detected in the spectral region 1300–1600 nm corresponding to the first overtone of water OH stretching vibrations. Furthermore, specific water spectral patterns (aquagrams) related to different water molecular conformations have been found along the course of protein nucleation and aggregation. Right in the beginning, dissociation of hydrogen-bonded network in bulk water and coinstantaneous protein and ion hydration were observed, followed by water hydrogen-bonded networks development, presumably forcing the nucleation. These specific transformations of water spectral pattern could be used further as a biomarker for early non-invasive diagnosis of amyloidoses prior to explosive amplification and deposits of amyloid fibrils.

Raman, infrared and near-infrared spectroscopic characterization of the herderite–hydroxylherderite mineral series

Natural single-crystal specimens of the herderite–hydroxylherderite series from Brazil, with general formula CaBePO4(F,OH), were investigated by electron microprobe, Raman, infrared and near-infrared spectroscopies. The minerals occur as secondary products in granitic pegmatites. Herderite and hydroxylherderite minerals show extensive solid solution formation. The Raman spectra of hydroxylherderite are characterized by bands at around 985 and 998cm−1, assigned to ν1 symmetric stretching mode of the HOPO33- and PO43- units. Raman bands at around 1085, 1128 and 1138cm−1 are attributed to both the HOP and PO antisymmetric stretching vibrations. The set of Raman bands observed at 563, 568, 577, 598, 616 and 633cm−1 are assigned to the ν4 out of plane bending modes of the PO4 and H2PO4 units. The OH Raman stretching vibrations of hydroxylherderite were observed ranging from 3626cm−1 to 3609cm−1. The infrared stretching vibrations of hydroxylherderites were observed between 3606cm−1 and 3599cm−1. By using a Libowitzky type function, hydrogen bond distances based upon the OH stretching bands were calculated. Characteristic NIR bands at around 6961 and 7054cm−1 were assigned to the first overtone of the fundamental, whilst NIR bands at 10,194 and 10,329cm−1 are assigned to the second overtone of the fundamental OH stretching vibration. Insight into the structure of the herderite–hydroxylherderite series is assessed by vibrational spectroscopy.

Comparing the rates of absorption and weight loss during a desorption test using near infrared spectroscopy

The importance of determining skin hydration has over the years prompt the development of many instruments and methods, specifically designed to assess this parameter or water contents especially in the stratum corneum, and have greatly matured to suit different anatomical sites and measure multiple attributes. Of those, Near Infrared Spectroscopy (NIRS) has gained wide interest as a precise, safe, fast and noninvasive technique for determining skin hydration due to its high sensitivity to hydrogen bonding and ability to measure the amount of water in skin directly using the intensities of overtone and combination bands of OH and HOH water bonds occurring in the NIR region, that are good indicators of the state of skin hydration. This paper reports near infrared spectrophotometric measurements using a highly sophisticated spectrophotometer in the region of 1000-2500nm to study the water uptake and dehydration properties of skin in vitro using samples of porcine skin. Initial results of pure liquid water and skin samples have clearly displayed the prominent bands associated with water content, and desorption tests have been able to verify changes in these bands associated with water content, although a clear correlation between the rates of weight loss and absorbance loss at various hydration periods has not yet been established. These preliminary results are expected to further explain the relationship between water and skin, and its role within, in hope to aid the future development of a portable instrument based on near infrared spectroscopy that would be capable of directly measuring skin hydration and/or water content in a fast and noninvasive manner.

Multidimensional local mode calculations for the vibrational spectra of OH−(H2O)2 and OH−(H2O)2·Ar

Multidimensional local mode calculations are performed for OH stretching vibrations of the gas phase OH(-)(H2O)2 and OH(-)(H2O)2·Ar clusters in the 1000-4000 cm(-1) energy range. The potential energies and the associated dipole moment values are calculated with MP2/6-311++G(3df,3pd). To fully take into account the anharmonic effects for the stretching vibrations of the ionic hydrogen bonded OHs (IHB OHs), those donating H to the O atom in OH(-), the vibrational Hamiltonian represented by the discrete variable representation (DVR) technique is diagonalized without using any truncation/contraction scheme for the basis. The necessary potential energies and dipole moment values at the DVR grid points are supplied by the polynomial inter- and extrapolations based on the values calculated at fine spatial grid points. We found that the peaks at 2700 cm(-1) should be assigned to the first overtone (ν: 0 → 2) of the IHB OH stretching vibrations rather than the previous assignment of the fundamental of the IHB OH based on harmonic frequencies. The relevant fundamental peaks should be observed around 1600-2000 cm(-1) where no experimental observation has been performed. This prediction of the fundamental peak positions leads to a simple correlation between the magnitude of the red-shift of the IHB OH stretching vibrational peak position and the cluster size of OH(-)(H2O)n for n = 1-3. Furthermore, to determine important contributions toward the assignment of the experimental spectrum, detailed analyses are performed from the following 3 viewpoints: (1) mode coupling between the inter water IHB OH stretching vibrations, (2) coupling between the IHB OH and the low-frequency OO stretching vibrations and (3) argon attachment to OH(-)(H2O)2. We found that the overall shape of the vibrational spectrum can be essentially described by considering only factor (1). However, fairly large peak shifts are caused by factors (2) and (3).

Application of Near-infrared Spectroscopy to the Quality Assurance of Ethanol and Butanol Blended Gasoline

The authors recorded near-infrared spectra of ethanol and butanol blended gasoline in the range of 5–30% of alcohol content. The major peaks in the spectra were assigned to the first CH overtone (~5670, ~5770, ~5810, and ~5870 cm−1), first OH overtone of alcohol (~6320 cm−1, 6720 cm−1), and second CH overtone (~8285, ~8400, and ~8690 cm−1). The OH overtone peak of the recorded spectra was subjected to the partial least squares (PLS) procedure to obtain calibration plots. The correlation coefficients (R 2) of .9938 and .9634 were obtained for the ethanol and butanol PLS calibrations, respectively. Recently there has been a great interest in butanol as a better gasoline blending alternative to ethanol. To understand the alcohol-gasoline interactions the integrated area of the polymeric OH alcohol band (~6320 cm−1) was plotted against the percentage of the alcohol content and the abrupt changes in the area were explained in terms of the viscosity of the fuel. Based on the OH integrated area plots the authors suggest that between 10 and 15% butanol can be blended with gasoline without compromising the viscosity of the fuel for optimum combustion. The results reveal that the near-infrared spectroscopy technique is a good alternative to the chromatographic methods for the quality assurance of the ethanol blended gasoline and in the future may find its application in the quality control of the butanol blended gasoline. The precision of the near-infrared quantification of ethanol and butanol is ±1%.

Assessment of Titratable Acidity in Fruit Using Short Wave near Infrared Spectroscopy. Part B: Intact Fruit Studies

Interactance spectra (700–1100 nm) of intact fruit possess features interpreted as being due to the dilution and perturbation of water OH stretching and combination bands (with the second and third overtones of OH stretching at 960 nm and 740 nm, respectively), while the contribution from citric acid CH2 and OH stretching and combination bands are not obvious. A model developed using interactance spectra collected from the cut surfaces of lime fruit (mean ± SD of 7.3 ± 0.51 g citric acid equivalents 100 mL−1, units subsequently presented as% w/v) achieved prediction results of RMSEP=0.16%, rp2 = 0.79, bias = −0.03%. However, for intact lime fruit, model calibration results ( RMSECV=0.16, rcv2 = 0.85) were markedly better than prediction results ( RMSEP=0.30, rp2 = 0.49). For a low total titratable acidity (TTA) product, peach (with spectra collected across fruit maturity stages; mean ± SD of 0.88 ± 0.17%), calibration results were relatively poor ( RMSECV=0.09%, rcv2 = 0.79) and the model failed in prediction ( RMSEP=0.10%, rp2 = 0.00, bias = 0.02%). It is concluded that interactance geometry shortwave (700–1100 nm) near infrared spectroscopy using diode array instrumentation and an interactance optical geometry suited to on-line or field-portable instrumentation used for Brix and DM assessment is not appropriate for assessment of the acidity of intact low TTA fruit and has limited use for high TTA fruit.

Assessment of Titratable Acidity in Fruit Using Short Wave near Infrared Spectroscopy. Part A: Establishing a Detection Limit Based on Model Solutions

Spectra (700–2500 nm) of citric acid dissolved in water possess features interpreted as being due to the dilution and perturbation of water OH stretching and combination bands (with the second and first overtones of OH stretching at 960 nm and 1420 nm, respectively, and a combination band of OH vibration at 2132 nm) and also to citric acid OH stretching and combination bands and citric acid CH2 bands (first overtone of CH2 stretching at 1680 nm and a combination band of CH2 at 2284 nm). A searching window method was used to optimise the wavelength region for a partial least squares (PLS) regression model development (around 743–904 nm for the region below 1100 nm). Despite the apparent lack of information below 1100 nm, a PLS regression model based on transmission spectra (743–904 nm) of pure citric acid—water mixtures (standard deviation = 6.65g citric acid 100 mL−1) yielded a root mean square error of cross-validation ( RMSECV) of 0.34% and correlation coefficient of determination ( Rcv2) = 0.998. However, if the matrix was varied with 0, 10 and 13% sucrose or fruit juice, RMSECV increased to 0.79%. This RMSECV value is proposed as a benchmark for attempts to assess titratable acidity of juice based on shortwave (700–1100 nm) near infrared spectra of intact fruit collected using silicon diode array instrumentation.

NIR and MIR spectroscopic characteristics of hydrophilic and hydrophobic bentonite treated with sulphuric acid

Near-infrared (NIR) and mid-infrared (MIR) spectroscopy are irreplaceable methods for characterization of bentonites. The paper presents work on bentonites modified with inorganic Na + and organic HDTMA + (hexadecyltrimethylammonium) cations and treated by 1.5, 3, 4.5 and 6 M H 2SO 4. The characterization was based on the assignment of the stretching ( ν) and bending ( δ) vibrations observed in the MIR region and the first overtone [2 ν(R–H)] and combination [ ν(R–H) + δ(R–H)] modes of R–H groups (R = O, C) in the NIR region. NIR spectrum shows the characteristic OH and CH bonds for organomontmorillonite. The effect of larger alkylammonium cations on the vibrations of Si–O and OH bonds in montmorillonite layers is observed. A few key-bands in the NIR region show the change of water in the interlayer montmorillonite. The intensities of the overtone (7080 and 6840 cm −1) and combination (5242 cm −1) bands of H 2O have considerably decreased as a result of hydrophobic character of the NaOM. Spectra of acid-treated samples show a gradual decrease in the intensities of the OH overtone (near 7100–7000 cm −1) and combination bands (4600–4300 cm −1) reflecting a fewer number of octahedral atoms. This paper also points out that ATR technique and the 2nd derivative spectrum enables much precise band assignment.